JP2011089520A - Model-based coordinated air-fuel control for gas turbine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suitably coordinate air and fuel supply quantities for gas turbine combustion. <P>SOLUTION: A fuel controller 33 provides a fuel control output signal 49 to a fuel control actuator 47 to control the operations. The fuel controller 33 determines the fuel control output signal 49 based on a rotational speed error and provides a combustion air control output signal 59 to a combustion air control actuator 61 to control the operations. A cross channel controller 15 communicates with the fuel controller 33 and a combustion air controller 35 and provides a combustion air control modification signal 67 to the combustion air controller 35. The combustion air control modification signal 67 is determined from the fuel control output signal 49 by using an air versus fuel model. The combustion air controller 35 determines a preliminary combustion air control signal 63 based on an exhaust temperature error, and further determines the combustion air control output signal 59 based on both of the preliminary combustion air control signal 63 and the combustion air control modification signal 67. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control system for a gas turbine, and more particularly to a control system having both a fuel controller and a combustion air controller.

  A gas turbine is typically coupled to and drives a generator. It is known to control the amount of fuel and air supplied to the combustion chamber of a gas turbine using a cross-channel controller. Known cross-channel controllers operate a turbine speed error signal that is an input to the fuel supply controller. Such a cross-channel controller processes the speed error signal and the resulting speed error signal is added to the turbine exhaust temperature error signal. The sum of the turbine exhaust temperature error signal and the processed speed error signal is processed by the air supply controller using a transfer function to generate a control signal that controls the air supplied to the combustion chamber. See, for example, US Pat. Nos. 5,487,265 (January 30, 1996) and 5,636,507 (June 10, 1997).

US Pat. No. 5,636,507

  According to one aspect, the present invention provides a control system for a gas turbine. The control system includes a fuel control actuator and a combustion air control actuator. The speed sensor detects the rotational speed of the gas turbine. The temperature sensor detects the exhaust temperature of the gas turbine. The coordinated air fuel controller controls the operation of the fuel control actuator and the combustion air control actuator. The coordinated air fuel controller receives a first input signal from the speed sensor and a second input signal from the temperature sensor. The rotational speed error calculator obtains a rotational speed error based on the first input signal from the speed sensor and the speed reference unit. The exhaust temperature error calculator obtains an exhaust temperature error based on the second input signal from the temperature sensor and the temperature reference unit. The fuel controller provides a fuel control output signal to the fuel control actuator to control operation of the fuel control actuator. The fuel controller obtains a fuel control output signal based on the rotation speed error. The combustion air controller provides a fuel control output signal to the fuel control actuator to control the operation of the fuel control actuator. The cross channel controller is in communication with the fuel controller and the combustion air controller. The cross channel controller provides a combustion air control correction signal to the combustion air controller. The cross channel controller determines a combustion air control correction signal from the fuel control output signal using an air-to-fuel model. A combustion air controller determines a pre-combustion air control signal based on the exhaust temperature error, and further determines a combustion air control output signal based on both the pre-combustion air control signal and the combustion air control correction signal.

  According to another aspect, the present invention provides a method for controlling air supply and fuel supply in a gas turbine. Obtain the rotational speed of the gas turbine. The rotational speed error is generated by comparing the rotational speed of the gas turbine with a speed reference. A fuel control output signal corresponding to the rotational speed error is generated. The fuel control output signal is provided to the fuel control actuator. A fuel control actuator adjusts the fuel flow rate based on the fuel control output signal. A cross-channel controller is provided that includes an air-to-fuel model. The cross channel controller generates a combustion air control correction signal from the fuel control output signal using an air-to-fuel model. Obtain the exhaust temperature of the exhaust gas from the gas turbine. The exhaust temperature error is generated by comparing the exhaust temperature with a temperature reference. A pre-combustion air control signal corresponding to the exhaust temperature error is generated. The pre-combustion air control signal and the combustion air control correction signal are combined to generate a combustion air control output signal. The combustion air control output signal is provided to a combustion air control actuator. A combustion air control actuator adjusts the amount of combustion air based on the combustion air control output signal.

  These and other aspects of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings.

1 is a schematic diagram of a gas turbine and a control system for the gas turbine. The graph which shows an inlet guide vane position vs. fuel streak standard.

  The features and aspects of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like elements. However, the present invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

  Various signals are discussed below. It should be understood that the signal can be an analog signal, a digital signal, or a data value stored in a storage area such as a register. Various circuits and portions of the circuits are discussed below. It should be understood that circuits and portions of circuits may be implemented by execution of program instructions by discrete electrical components, integrated circuits, and / or processors.

  A problem with known gas turbine coordinated air fuel controllers is that the coordination of inputs to the air supply and fuel supply controller does not necessarily coordinate their output air and fuel requirements, respectively. One reason for this is that the relationship between turbine speed error and turbine exhaust temperature error is not intuitive, making cross-channel controller design and adjustment difficult. Another reason is that constraints in the fuel supply controller may cause the turbine speed error to be inadequate as an indication of an upcoming fuel supply change.

  Known cross-channel controllers operate in a “control error space” that links speed and exhaust temperature errors. However, it is difficult to obtain an accurate relationship between the speed error and the exhaust temperature error. A more preferred approach is to operate the cross-channel controller in a “request space” that is placed after each control transfer function operates with an error signal in the control channel. The cross-channel controller in the demand space can coordinate the air and fuel supply using a direct relationship between air and fuel, such as an air-to-fuel model. The exact relationship between air and fuel can be determined more easily than the exact relationship between speed error and exhaust temperature error. Thus, a coordinated air fuel controller having a cross-channel controller located in the required space can be designed and adjusted more easily than known cross-channel controllers. Further, by having the cross channel controller in the request space, it becomes possible to reflect the constraints in the fuel supply controller.

  FIG. 1 is a schematic diagram of a gas turbine 11 and a coordinated air fuel controller 13 for the gas turbine. The gas turbine 11 has an associated speed sensor 17 that detects the rotational speed of the gas turbine (ie, the actual rotational speed or a representative speed). The speed sensor 17 provides a turbine speed feedback signal 21 as an input to the controller 13. The gas turbine 11 also has a temperature sensor 23 that detects the temperature of the exhaust gas of the gas turbine. The temperature sensor 23 provides an exhaust temperature feedback signal 25 as an input to the controller.

  The gas turbine 11 drives a generator 27. One or more sensors 29 can provide an input signal to the controller 13 associated with the electrical load on the generator. The sensor 29 can provide a load signal 31 such as an electrical level, for example.

  Next, the cooperative air fuel controller 13 will be examined in detail. The coordinated air fuel controller 13 can include sub-controllers such as a cross channel controller 15, a fuel controller 33, and a combustion air controller 35. The controller 13 can be an electrical controller and can include one or more processors. For example, the controller 13 may be one of a microprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate array (FPGA), discrete logic, or the like More can be included. The controller 13 can further include a memory, and can store program instructions that provide functionality that is considered to be attributed to the controller herein. The memory can include read only memory (ROM), random access memory (RAM), electrically erasable programmable ROM (EEPROM), flash memory, or the like. One or more volatile, non-volatile, magnetic, optical, or electrical media can be included. The controller 13 can further include one or more analog-to-digital (A / D) converters for processing various analog inputs to the controller.

  The controller 13 includes a rotational speed error calculator 37 and a speed reference unit 39. The rotational speed error calculator 37 obtains a rotational speed error based on signals from the speed sensor 17 and the speed reference unit 39. For example, the rotational speed error calculator 37 compares the turbine speed feedback signal 21 with the speed reference unit 39 and outputs a rotational speed error signal 41. In one embodiment, the rotational speed error calculator 37 calculates the difference between the turbine speed feedback signal 21 and the speed reference 39. The speed reference unit 39 can change over time in response to the changed operating conditions.

  Optionally, a load signal 31 in addition to the turbine speed feedback signal 21 is provided to the rotational speed error calculator 37 to improve load regulation. The controller 13 can include a droop filter 43 along the load signal 31 between the sensor and the rotational speed error calculator 37. The droop filter 43 converts the load signal 31 into a speed signal so that the rotation speed error calculator 37 can be used. The conversion by the droop filter 43 is based on the system frequency of the power network to which the generator 27 is connected.

  The rotational speed error signal 41 is provided to the fuel controller 33. An optional deadband filter 45 can be placed between the rotational speed error calculator 37 and the fuel controller 33 to prevent undesired operation of the fuel control actuator 47 based on small speed errors. The fuel controller 33 provides a fuel control output signal 49 to the fuel control actuator 47 to control the operation of the fuel control actuator. The fuel control actuator 47 is responsive to the fuel control output signal 49 to control the amount of fuel provided to the combustion chamber of the gas turbine. The fuel control actuator 47 can control the fuel stroke 73 of one or more fuel valves based on, for example, a fuel stroke reference (FSR) signal from the fuel controller 33. The fuel controller 33 controls the amount of fuel provided to the combustion zone by controlling the operation of the fuel control actuator 47.

The fuel controller 33 receives the rotational speed error signal 41 and processes the error signal to generate a fuel control output signal 49. In one embodiment, the fuel controller 33 processes the rotational speed error signal 41 using the transfer function K ₁ (s) 51. For example, the fuel controller 33 can generate a fuel control output signal 49 from the rotational speed error signal 41 by implementing a proportional integral (PI) control method. In the PI control method, the transfer function K ₁ (s) 51 includes a proportional term having a proportional gain and an integral term having an integral gain. Alternatively, the fuel controller 33 can implement a proportional integral derivative (PID) control scheme, or can implement other control schemes.

  The controller 13 includes an exhaust temperature error calculator 53 and a temperature reference unit 55. The exhaust temperature error calculator 53 obtains an exhaust temperature error based on signals from the temperature sensor 23 and the temperature reference unit 55. For example, the exhaust gas temperature error calculator 53 compares the exhaust gas temperature feedback signal 25 with the temperature reference unit 55 and outputs an exhaust gas temperature error signal 57. In one embodiment, the exhaust temperature error calculator 53 calculates the difference between the exhaust temperature feedback signal 25 and the temperature reference unit 55. The temperature reference 55 changes over time in response to changed operating conditions, such as changes in the amount of fuel supplied to the combustion zone of the gas turbine.

  The exhaust temperature error signal 57 is provided to the combustion air controller 35. The combustion air controller 35 provides a combustion air control output signal 59 to the combustion air control actuator 61 to control the operation of the combustion air control actuator. The combustion air control actuator 61 controls the amount of air provided to the combustion chamber of the gas turbine in response to the combustion air control output signal 59. The combustion air control actuator 61 can control the position (for example, angle) of the inlet guide vane of the gas turbine, for example. The combustion air controller 35 controls the amount of air provided to the combustion zone by controlling the operation of the combustion air control actuator 61.

The combustor controller 35 receives the exhaust temperature error signal 57 and processes the error signal to generate a pre-combustion air control signal 63. In one embodiment, the combustion air controller 35 processes the exhaust temperature error signal 57 using a transfer function K ₂ (s) 65. For example, the combustion air controller 35 can implement a PI control scheme and generate the pre-combustion air control signal 63 from the exhaust temperature error signal 57. Alternatively, the combustion air controller 35 can implement a PID control scheme or implement another control scheme.

  The cross channel controller 15 operating in the required space portion of the coordinated air fuel controller 13 communicates with both the fuel controller 33 and the combustion air controller 35. The cross channel controller 15 receives the fuel control output signal 49 from the fuel controller 33 and calculates the combustion air control correction signal 67 based on the fuel control output signal. The cross channel controller 15 provides a combustion air control correction signal 67 to the combustion air controller 35.

  The combustion air controller 35 receives the combustion air control correction signal 67 from the cross channel controller 15. The combustion air controller 35 determines a combustion air control output signal 59 based on both the pre-combustion air control signal 63 and the combustion air control correction signal 67. For example, the combustion air controller 35 may include an adder circuit 69 that combines the pre-combustion air control signal 63 and the combustion air control correction signal 67 to determine the combustion air control output signal 59. The pre-combustion air control signal 63 and the combustion air control correction signal 67 can be added together by an adder circuit 69, and the output of the adder is a combustion air control output signal 59. Other methods besides simple sums can be used to combine the pre-combustion air control signal 63 and the combustion air control correction signal 67. For example, this combination can be implemented by an algorithm that weights one input higher than the other depending on the situation.

  The combustion air control correction signal 67 functions to coordinate the operations of the fuel controller 33 and the combustion air controller 35. Such coordination can reduce the possibility of causing various adverse situations of the gas turbine. For example, such coordination can reduce the likelihood of lean blowout, exhaust superheat temperature, and compressor surge.

  Here, the cross channel controller 15 will be described in detail. The cross channel controller 15 includes an air-to-fuel model. The cross channel controller 15 calculates the combustion air control correction signal 67 from the fuel control output signal 49 using the air-to-fuel model. For example, as shown in FIG. 2, the air-to-fuel model 71 can associate an inlet guide vane position (IGV) with a fuel stroke reference (FSR). Alternatively, the air-to-fuel model can directly relate the air flow to the fuel flow. For a given fuel control output signal 49, the cross-channel controller 15 determines and outputs a corresponding combustion air control correction signal 67 using an air-to-fuel model. It should be understood that the air-to-fuel model can be implemented by mathematical algorithms, by look-up tables, or by other known model techniques.

  As shown in FIG. 2, the air-to-fuel model 71 can define a steady state correlation between the FSR and IGV. Accordingly, the air-to-fuel model 71 is a steady state model. The cross channel controller 15 outputs the combustion air control correction signal 67 and maintains the operation of the gas turbine 11 substantially along the steady state path 72 shown. Deviations from the steady-state path (eg, IGV values that are too large or too small for a given FSR), as schematically shown by the curved arrows in FIG. 2, result in a lean blowout. It can lead to adverse conditions such as exhaust overheating temperature and compressor surge.

  In FIG. 2, the steady state path 72 is piecewise linear. Steady state path 72 has a horizontal portion where the IGV is constant over the low region FSR. After the horizontal portion, the steady state path 72 has a constant positive slope with increasing FSR. It should be understood that a steady state path can have a curved portion or a combination of straight and curved portions.

  The air-to-fuel model 71 shown in FIG. 2 is a steady model. It should be understood that the cross-channel controller 15 may use other models in determining the combustion air control correction signal 67, such as a transient model or a combination of steady state and transient models.

  In the embodiment of FIG. 1, the cross-channel controller is not shown in operation in the control error space. However, if necessary, an additional cross-channel controller may be provided in the control error space.

  The embodiment of FIG. 1 includes a separate fuel and air control loop and cross-channel controller 15. In further embodiments, separate fuel and air control loops and cross-channel controllers are replaced with multi-input multi-output controllers that implement control algorithms that provide the functions described herein.

  It is to be understood that the present disclosure is illustrative only and various changes can be made by adding, modifying, or excluding details without departing from the fair scope of the teachings contained in the present disclosure. Accordingly, the invention is not limited to the specific details of the disclosure except to the extent that the following claims are necessarily limited.

11 Gas Turbine 13 Coordinated Air Fuel Controller 15 for Gas Turbine 15 Cross Channel Controller 17 Speed Sensor 23 Temperature Sensor 27 Generator 29 Sensor 37 Rotational Speed Error Calculator 39 Speed Reference Unit 43 Droop Filter 45 Dead Band Filter 47 Fuel Control Actuator 53 Exhaust Temperature Error Calculator 55 Temperature Reference Unit 57 Exhaust Temperature Error Signal 59 Combustion Air Control Output Signal 61 Combustion Air Control Actuator

Claims (12)

A control system for a gas turbine (11),
A fuel control actuator (47);
A combustion air control actuator (61);
A speed sensor (17) for detecting the rotational speed of the gas turbine (11);
A temperature sensor (23) for detecting the exhaust temperature of the gas turbine (11);
A coordinated air fuel controller (13) for controlling the operation of the fuel control actuator (47) and the combustion air control actuator (61);
With
The coordinated air fuel controller (13) receives a first input signal from the speed sensor (17) and a second input signal from the temperature sensor (23);
The coordinated air fuel controller (13) further includes:
A rotational speed error calculator (37) for determining a rotational speed error based on the first input signal from the speed sensor (17) and the speed reference unit (39);
An exhaust temperature error calculator (53) for obtaining an exhaust temperature error based on the second input signal from the temperature sensor (23) and the temperature reference section (55);
A fuel control output signal (49) is provided to the fuel control actuator (47) to control the operation of the fuel control actuator (47), and the fuel control output signal (49) is obtained based on the rotational speed error. A controller (33);
A combustion air controller (35) for providing a combustion air control output signal (59) to the combustion air control actuator (61) to control the operation of the combustion air control actuator (61);
A cross-channel controller (15) in communication with the fuel controller (33) and the combustion air controller (35);
Including
The cross-channel controller (15) provides a combustion air control correction signal (67) to the combustion air controller (35);
The cross channel controller (15) determines a combustion air control correction signal (67) from the fuel control output signal (49) using an air-to-fuel model (71);
The combustion air controller (35) obtains a pre-combustion air control signal (63) based on the exhaust temperature error, and further calculates the pre-combustion air control signal (63) and the combustion air control correction signal (67). Determining the combustion air control output signal (59) based on both;
Control system. The air-to-fuel model (71) is a steady state model;
The control system according to claim 1. The fuel controller (33) processes the rotational speed error using a fuel control transfer function including a proportional gain and an integral gain to obtain a fuel control output signal (49), which is obtained as the fuel control actuator (47). And the cross-channel controller (15), wherein the combustion air controller (35) processes the exhaust temperature error using a combustion air control transfer function to determine a pre-combustion air control signal (63).
The control system according to claim 1. The cross-channel controller (15) operates in a demand space portion of the cooperative air fuel controller (13);
The control system according to claim 3. The combustion air control actuator (61) controls a portion of the inlet guide vane;
The control system according to claim 1. The fuel control actuator (47) controls a fuel stroke (73) and the air-to-fuel model (71) provides a steady state relationship between the fuel stroke (73) reference and the position of the inlet guide vane. To
The control system according to claim 5. A method for controlling air supply and fuel supply in a gas turbine (11), comprising:
Determining the rotational speed of the gas turbine (11);
Generating a rotational speed error by comparing the rotational speed of the gas turbine (11) with a speed reference;
Generating a fuel control output signal (49) corresponding to the rotational speed error;
Providing the fuel control output signal (49) to a fuel control actuator (47);
The fuel control actuator (47) adjusting a fuel flow rate based on the fuel control output signal (49);
Providing a cross-channel controller (15) including an air-to-fuel model (71);
The cross-channel controller (15) generating a combustion air control correction signal (67) from the fuel control output signal (49) using the air-to-fuel model (71);
Obtaining an exhaust temperature of the exhaust gas of the gas turbine (11);
Generating an exhaust temperature error by comparing the exhaust temperature with a temperature reference (55);
Generating a pre-combustion air control signal (63) corresponding to the exhaust temperature error;
Combining the pre-combustion air control signal (63) and the combustion air control correction signal (67) to generate a combustion air control output signal (59);
Providing the combustion air control output signal (59) to a combustion air control actuator (61);
The combustion air control actuator (61) adjusts the amount of combustion air based on the combustion air control output signal (59);
Including methods. The air-to-fuel model (71) is a steady state model;
The method of claim 7. Generating the fuel control output signal (49) includes processing the rotational speed error using a fuel control transfer function including a proportional gain and an integral gain to generate a pre-combustion air control signal (63). The step includes processing the exhaust temperature error using a fuel control transfer function;
The method of claim 7. The method further includes providing a coordinated air fuel controller (13) that includes both a fuel controller (33) and a combustion air controller (35), wherein the cross-channel controller (15) is a requirement of the coordinated air fuel controller (13). Works in space,
The method of claim 9. Adjusting the amount of combustion air by the combustion air control actuator (61) includes adjusting the position of the inlet guide vane.
The method of claim 7. The step of adjusting the fuel flow rate by the fuel control actuator (47) includes the step of adjusting the fuel stroke (73), and the air-to-fuel model (71) further includes a fuel stroke (73) reference and the inlet guide vane. Providing a steady state relationship between the position of
The method of claim 11.

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